1. Field of the Invention
The present invention relates to an illumination assembly, more particularly to an illumination assembly having a multi-chip light emitting diode (LED) array.
2. Description of the Related Art
White light may be obtained using LEDs by combining a LED with other materials, or by combining a plurality of differently colored LEDs. As an example of the former method, a blue LED is used in conjunction with a phosphor powder that emits a yellow light when excited. The yellow light emitted by the phosphor powder mixes with the blue light of the LED that has not been absorbed by the phosphor powder to generate white light. In the latter method, an additive color technique is employed by using differently colored LEDs in combination, thus obtaining white light. That is, white light is obtained by combining light irradiated from red, green, and blue LEDs. Two different conventional configurations employing this latter approach are described below.
FIG. 1 schematically shows a conventional LED cluster arrangement. LEDs are arranged in a matrix of a plurality of RGB (or RGGB) clusters 10 to thereby utilize the additive color phenomenon to obtain white light. In this configuration, if it is desired to obtain a brightness roughly equal to that obtained using, for example, a cold cathode fluorescent lamp, a large number of the LEDs need to be used, thus raising costs. Further, if a small number of the LEDs in the cluster arrangement malfunction, the purity of the white light is reduced, and other non-white colors may become visible. In addition, with this configuration, a color combination distance (i.e., a minimum distance from the LEDs at which the additive color phenomenon takes effect) is approximately 30 mm, which may be considered excessive for some applications.
FIG. 2 is a perspective view of a conventional multi-chip LED unit. In the particular configuration shown in the drawing, three discrete red, green, and blue LEDs 11 are integrated in a single package. The LEDs 11 realize a Lambertian light distribution so that white light is obtained by combining light of the LEDs 11. A cylindrical transparent lens (not shown) is typically used in the multi-chip LED unit to enhance light-emission efficiency. However, since it is not possible for all three of the LEDs 11 to be positioned on a center axis of the transparent lens, the light emitted from each of the LEDs 11 is skewed in three different directions and is not projected vertically. As a result, the color combination distance is increased, and the additive color effect is degraded.